1. Field of the Invention
The present invention relates generally to the field of enamelled or glassed metal vessels used in the chemical processing industry and specifically to such vessels which include metal jackets surrounding significant portions of the shells thereof which are enameled or glassed on their interiors.
2. Background
Enamelled or glassed metal vessels are well known and used commonly in the chemical processing industry to contain chemical reactions and/or other chemical processing steps in the manufacture of a wide variety of chemical substances and mixtures. Such vessels are coated on thin interiors with enamel or glass to prevent corrosion, erosion and the effects of elevated and/or decreased temperatures to come into contact with the underlying metal shell of the vessel.
The enamelling or glassing materials, usually in the form of colloidal suspensions, are sprayed onto the interior metal surfaces of the vessel which have been previously prepared to accept those enamelling or glassing materials and to cause them to adhere to those metal surfaces.
Then the vessels are subjected to elevated temperatures, for example, as is provided by a furnace, to "fire" or fuse the enamelling or glassing material to the underlying metal surfaces of the vessel. Such firing, usually to some degree, distorts the shape of the metal shell, but within still acceptable ranges of size and shape in respect to the overall chemical reactor system.
Many such metal vessels are then encased in a metal jacket. The purpose of the jacket, for example, may be to enclose insulation materials around the interior of the vessel shell. Or, for example, the purpose of the jacket may be for structural support of the vessel shell. There is, in any case, usually a more or less uniform gap between the exterior surface of the vessel shell and the interior surface of the metal jacket.
When metal jackets are used on reaction vessels, they must be attached to the exterior of the vessel shell. This is usually done by welding. But the jacket cannot be welded directly to the exterior surface of the metal shell because the localized heat imposed by welding will cause localized distortion, stresses and expansion and contraction of the metal of the vessel shell. Such tends greatly to cause the enamelling or glassing on the interior surface of the vessel shell to crack and, in many cases, fall off.
To avoid such destruction of the enamelled or glassed interior surfaces of the vessel shell, welding rings are attached, usually by welding, to the exterior of the vessel shell before the interior of that vessel shell is enamelled or glassed. The purpose of the welding rings is to provide a metal surface, relatively remote from the metal shell itself, to which the jacket can be welded without imposing the localized heat of welding directly to the area of the exterior of the metal shell adjacent to an enamelled or glassed interior surface of that shell.
Because of the required heating of the shell, to fuse the enamelling or glassing materials to the interior thereof, as mentioned before, distortion of the shell is caused. When welding rings are attached to the exterior surface of the shell prior to firing, the welding rings, likewise, distort when the shell is fired. This distortion of the welding rings causes problems, after the shell is enamelled or glassed, in fitting the jacket to those welding rings in preparation for welding. Because of distortion, gaps are caused erratically and intermittently at the fit of the jacket edges to the welding ring. These gaps necessitate that manual welding be carefully done to lay in a root pass of welding metal which fills those gaps. Once the root pass is in place, ensuring a continuous metal to metal joint of thew jacket to the weld rings, automatic welding techniques, such as submerged arc welding, can be used to lay in the additional weld metal filler to ensure a strong and solid joint. Needless to say that the need for a normal welding root pass requires much additional time and care, using highly trained welders, before the automatic welding methods can be applied.
Thus, there is a need for a means by which the above described gaps can be diminished or reduced to the point that the root welding pass can, also, be applied by automatic welding techniques, thus eliminating the need for an extended time period for manual welding performed by costly trained welders.